1. Field of the Invention
The present invention generally relates to a laser apparatus and more particularly to a laser apparatus wherein end faces of the laser medium disposed between a pair of reflection mirrors are excited by a pumping light beam applied from a laser light source such as a semiconductor laser element or the like to thereby oscillate and radiate a laser light.
2. Description of the Prior Art
There is known in the art a solid state laser apparatus which is so constructed that a laser rod or laser medium made of Nd:YAG etc. is disposed between a pair of reflection mirrors and the end faces of the laser rods are excited by a pumping light beam applied from a laser light source such as a semiconductor laser element to thereby oscillate and radiate a laser light.
However, in this conventional solid state laser apparatus, a thermal lens is formed in the laser rod since the rod is heated by the pumping light beam, so that conventionally it has been intended to compensate for the thermal lens by providing a concave lens.
A focal length of the thermal lens, however, changes depending on the change of an amount of light of the pumping light beam for exciting the laser rod, so that it has been required to compensate for the thermal lens formed in the laser rod by selecting a concave lens for the compensation of the thermal lens having a suitable focal length depending on that of the thermal lens and further by adjusting relative position of the compensation concave lens or reflection mirrors with respect to the laser rod on an optical axis.
Thus, the conventional solid state laser apparatus has required, in order to compensate for the thermal lens formed in the laser rod, the selection of a concave lens for the compensation of the thermal lens having a suitable focal length depending on that of the thermal lens and further the adjustment of the relative position of the compensation concave lens or reflection mirrors with respect to the laser rod on the optical axis.